Surgical gowns, drapes and the like protect surgically prepared areas of the skin from contamination and also protect the surgeons and nurses against contamination through contact with unprepared or contaminated areas of the patient's skin. The surgical gown should present a sterile barrier to protect the patient from contamination through contact with the surgeon.
Liquid imperviousness of the gown or drape is recognized as an important property in assuring that the gown or drape presents a sterile surface and acts as a barrier to the passage of bacteria. If blood and other liquids strike through the surgical drape and contact the skin of the patient, bacteria which are deposited on the surface of the drape may be wicked through the capillary channels to the skin of the patient, and bacteria present on the skin of the patient may be wicked outward through capillary channels to the outer surface of the drape and the surgeon's gown may become contaminated by contact with the drape. In the case of the surgical gown, by a similar process, liquids may be wicked through to the skin of the surgeon.
Surgical gowns and drapes have been made from a variety of materials, nine of which will be compared hereinbelow with the laminate of this invention. Linen, muslin and other woven fabrics are common reusable materials. Nonwoven, fibrous disposable sheets are known. U.S. Pat. No. 3,410,266 discloses a laminated fabric construction in which a liquid-impervious, organic plastic film is sandwiched between liquid repellant fibrous sheets.
Fabrics and papers treated with water repellants such as silicone, fluorocarbons and other water repellants are known. Gowns constructed of plastic and waterproofed or water repellant paper are disclosed in U.S. Pat. No. 3,218,649.
In addition to being liquid repellent and a bacteria barrier, hospital gowns desirably present a non-glare outer surface, are nonlinting, possess antistatic characteristics and, not least importantly, are comfortable to the surgeon. U.S. Pat. Nos. 3,349,285 and 3,011,172 disclose elaborate means for electrically grounding gowns to render them antistatic in the potentially explosive atmosphere of an operating theatre.
Laminated materials which are waterproof and breathable and which are especially suited for use in rainwear or tents are disclosed in U.S. Pat. No. 4,194,041, assigned to the same assignee as the present application. That invention provides a layered article, for use in waterproof garments or tents, that is waterproof, resistant to surface active agents in perspiration, and that still permits the evaporation of perspiration and the transfer of moisture vapor through the layered article.
That invention comprises a combination of at least two layers: (1) an interior, continuous hydrophilic layer that readily allows water to diffuse through, prevents the transport of surface active agents and contaminating substances such as those found in perspiration, and is substantially resistant to pressure induced flow of liquid water; and (2) a hydrophobic outer layer that permits the transmission of water vapor and provides thermal insulating properties even when exposed to rain.
Garments made of those materials are permanently waterproof from exterior water sources yet allow the evaporation of perspiration whenever the partial pressure of water vapor inside the garment exceeds that outside.
The hydrophilic film used in the invention of U.S. Pat. No. 4,194,041 has a moisture vapor transmission rate exceeding 1000 gms./m.sup.2. day, and preferably above about 2000 gms./m.sup.2. day, permits no detectable transmission of surface active agents and preferably permits no detectable flow of liquid water at hydrostatic pressures up to 25 psig.
The hydrophobic layer used in that invention has a moisture vapor transmission rate exceeding 1000 gms./m.sup.2. day and preferably exceeding 2000 gms./m.sup.2. day, and an advancing water contact angle exceeding 90 degrees, and is preferably formed of a porous hydrophobic polymer.
It has been widely recognized that garments must be "breathable" to be comfortable. However, it is not necessary that air pass through the garment for it to be comfortable, only that water vapor from perspiration be transmitted from inside to outside so that undergarments do not become wet and so that the natural evaporative cooling effect can be achieved. Breathability and ability to transport interior moisture vapor to the external environment are used interchangeably in this discussion.
The transport of water through a layer can be achieved in a number of ways. Wicking is the most common when large quantities of moisture are to be transferred. Wicking materials are hydrophilic in that a drop of water placed on the surface of those materials forms an advancing water contact angle of less than 90 degrees so that they wet spontaneously. They are also porous with pores that interconnect to make complete pathways through the wicking material. Liquid water moves by capillary action from interior surface to exterior surface where it evaporates. Although some wicking materials may resist pressure induced flow of liquid water through them due to the tortuousity and length of flow path, they readily transport liquids by capillary action from the exterior surface to the interior surface and so are unsuitable for hospital gowns. The comfort attributed to cotton garments results from its ability to transport water to the exterior surface where it can readily evaporate and provide cooling. Another natural wicking material is leather which owes its great comfort to breathability via wicking.
The inventions disclosed in U.S. Pat. Nos. 3,953,566 and 4,194,041 have provided porous membranes that satisfy the two comfort requirements of being waterproof while also being permeable to the flow of water vapor. These membranes are usually laminated to fabrics for mechanical protection and style. The membranes are inherently hydrophobic and contain very small pores that resist the entry of liquid water even at substantial pressures or when rubbed or flexed, but readily allow the flow of gases, including water vapor. Unlike wicking materials, breathability is achieved by evaporation of liquid water inside the garment or on the inner surface of the membrane followed by gaseous flow or diffusion of water vapor through the membrane to the outside.